Processes for treating ferrous metals before drawing through dies



Patented Aug. 23, 1949 PROCESSES FOR TREATING FERROUS METALS BEFORE DRAWING THROUGH DIES Harry R. Spence and Horace W. Hooker, lLewlston, N. Y., assignors to Hooker Electrochemical Company, Niagara Falls, N. Y., a corporation of New York No Drawing. Application July 25, 1945,

Serial No. 607,102

5 Claims. 1

Our invention relates more particularly to a process for modifying the oxide on the surface of ferrous metals and their alloys which are in process 0f being rolled out into tubes, wires, bars or other shapes at elevated temperature, so that it takes on properties that adapt it to retain the lubricant for the dies in further drawing operations at lower temperatures.

Among the ferrous metals that may be treated in accordance with our process, besides iron, are the other metals of the ferrous group, including nickel and cobalt, and their alloys with each other and with chromium, manganese, molybdenum, tungsten, vanadium and copper, including the stainless steels containing nickel and chromium and alloys of nickel with chrom um, such as nichrome and Tophetfl which may contain little or no iron also alloys of nickel with copper, such as Monel, which contains no iron.

The drawing of metal generally involves heating it and passing it through rolls, at temperatures sufiiciently elevated to soften the metal. At these temperatures the metal picks up oxygen from the air and forms the'dark ferroso-ferric oxide. In the course of the working, the metal becomes toughened and hardened and the oxide film pressed into it until it may form a dense coal black glaze. There may also be several finishing passes at lower temperatures, such as ordinarily result from the work of friction and deformation. For this purpose it is generally necessary to remove the glaze; and also at intervals to anneal the metal. Removal of the glaze is diflicult, especially in the ease of the alloy steels. Annealing reoxidizes the metal. After the removal of the glaze, the clean deoxidized metal is passed through powdered lime or molten lead, with which it becomes lightly coated. Lubricant, such as soap or oil of high film strength, is then applied to the surface. The coating with lime or lead is necessary to cause adherence of the lubricant. In general the lime coating step must be repeated before each pass. When lead is used, it must afterward be removed by drastic pickling in strong acid, and the steps of coating with lead and pickling may have to be alternated several times in drawing out a single tube or wire.

Inco-pending application, Serial No. 538,538, filed June 2, 1944, now Patent No. 2,395,694, reissued as Patent No. Re. 22,887, there is disclosed a process for modifying the oxide glaze so that it is converted to a dark mat surface in which condition the oxide may be readily removed by a quick dip in dilute acid.

We now find that if the metal be subjected to this treatment in accordance with our process, but without the acid dip, the resulting dark mat surface will take and hold the lubricant without the coating of lime or lead. The metal is then ready to be passed through the next die. If more than one finishing pass is desired, successlve passes up to as many as three may be carried out by simply relubricating the dark mat surface before each pass. Our process, therefore, eliminates the coatings with lime or lead, preparatory to lubricating; also, when lead has been used, the drastic pickling in strong acid to remove it.

Our process comprises soaking the article in a bath of fused caustic alkali containing 1 to 20 per cent, and preferably 5 to 10 per cent, of an active oxidizing agent, at a temperature between 300 and 600 and preferably at about 500 C., depending upon the oxidizing agent, for 1 to 25 minutes, the time depending on caustic alkali and oxidizing agent used and upon the proportion of oxidizing agent in the bath. This treatment changes the physical character of the oxide so that the glaze is puffed out into a coating oi. fine grain, which may resemble lamp black. In some cases. however, the surface is brown and if the treatment is continued, the brown oxide eventually becomes so puffed out and loosened that some of it may be shaken off. The resulting powder is of the fineness of paint pigment.

Our fused alkali bath may consist of caustic soda, caustic potash or a mixture of these alkalies with each other or with'their carbonates. The

presence of the oxidizing agent lowers the melting point of the bath. Thus, 10 per cent of sodium nitrate lowers the melting point of caustic potash from 360 to 315 C. Also, by proper proportioning of a mixture of alkalies, it is possible to produce a bath of substantially lower melting point than that of any one of its individual components.

Thus a mixture of commercial caustic soda and caustic potash in equal proportions by weight melts at 205 0., whereas these alkalies, in comoxidizing acid, such as 1 to 20 per cent hydrochloric acid, preferably at 65 to 85 C. It is desirable to wash ofi excess caustic alkali before the acid dip. When this is done, there is less consumption'of acid. 7

Example! A piece of the same rod as that of Example I was treated in the same way except that the temperature was 500 C. and the time minutes. The result was substantially the same. This at present represents preferred practice.

Example III A piece of the same red as that of Example I was treated in the same way except that the temperature was 420 C. and the time 15 minutes. The result was substantially the same. A comparison of this example with the two preceding I shows that the time of treatment in our process is a function of the temperature of the bath.

Example IV Another piece of the same rod was immersed for 10 minutes in a fused bath of caustic soda and caustic potash in equal proportions by weight containing 10 per cent sodium nitrate at 400 It was little affected. This is believed to show that the caustic alkali is essential.

Example X Example XI A strip of nichrome containing 80 per cent nickel and-20 per cent chromium and no iron, heavily coated with dark oxide, was immersed in the same bath as in Example III for the same time and at the same temperature.

All pieces of metal treated as in Examples 1 to VII, X and XI came from the treatment described with mat surfaces having excellent lubricant retaining properties.

Although we have emphasized treatment of alloy steels, that is-only because they present the greatest diiiiculty. A large field of application is of course that of ordinary low or high carbon steels.

While we do not wish to be held to any particular theory as to the reactions that take place in our process, it would seem that the fused caustic alkalies form the corresponding salts of the a metal oxides, which are generally black, but some- C. The rod came out resembling those of Exam ples I to III.

Example V Example VI Another piece of the same rod as that treated in Example I was immersed in a bath of fused caustic potash containing 10 per cent sodium nitrate by weight for 4 minutes at 420 C. It came out with the oxide converted to a brown coating resembling that of Example V.

Example VII Another piece of the same rod was immersed for 6 minutes in a bath of fused caustic potash containing 10 per cent of potassium chlorate by weight at 420 C. It came outwith the oxide converted to a condition resembling that of Example V.

Example VIII Another piece of the same rod was immersed in a fused bath of caustic soda and caustic potash in equal proportions by weight.'without any oxidizing agent,-at 400 C. for 10 minutes. It came out a very dark brown in color, but without the desired mat surface.

Example IX Another piece of the same rod was immersed in a bath of fused sodium nitrate alone for 6 minutes and given a water wash and acid dip.

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times a very distinctive reddish brown; and these salts are quasi-molecular and retentive of lubricants. The presence of the oxidizing agent would promote formation of these salts. On the other hand, the presence of any considerable quantity of water would prevent the necessary temperature from being reached and perhaps operate adversely in other ways.

We claim as our invention:

1. In the drawing of tubes, rods, wires and the like, of ferrous metals, by ,passing the same through rolls at elevated temperatures, while exposed to atmospheric oxidation, resulting in formation of a dense, firmly adherent dark oxide glaze on the surface thereof, and by ubsequently lubricating the article by applying an ungent thereto, and passing it through dies at temperatures such as result from the work of friction and deformation; the improvement which comprises subjecting the surface, still coated with said oxide glaze, preparatory to lubricating it for a pass through the dies, to the action of a fused substantially anhydrous bath composed of at least one caustic alkali of the group consisting of sodium and potassium hydroxide and 1 to 20 per cent of at least one oxidizin agent of the group consisting of the alkali metal and alkali earth chlorates, peroxides, nitrates, dlchromates. manganates, and permanganates, at 300 to 600 C., for a time sufficient to convert the glaze to a coating with a mat surface having'lubricant-retaim ing properties.

2. .In the drawing of tubes, rods, wires and the like, of metals of the group consistin of iron, nickel and cobalt and their alloys with each other and with chromium, manganese, molybdenum, tungsten, vanadium and copper, by passing the same through rolls at elevated temperatures, while exposed to atmospheric oxidation, resulting in formation of a dense, firmly adherent dark oxide glaze over the surface thereof, and by subsequently lubricating the article, by applying an ungent thereto, and passing it through dies at temperatures such as result from the work of friction and deformation; the improvement which comprises subjecting the surface, still coated with said oxide glaze, preparatory to lubricating it for a pass through the dies, to the action of a fused substantially anhydrous bath composed of an alkali metal hydroxide and 1 to 20 per cent of at least one oxidizing agent of the group consisting of the alkali metal and alkali earth chlorates, peroxides, nitrates, dichromates, manganates and permanganates at 300 to 600 C., for a time sufficient to convert the glaze to a coating with a mat surface, having lubricant-retaining properties.

3. In the drawing of tubes, rods, wires and the like, of stainless" steel, by passing the same through rolls at elevated temperatures, while exposed to atmospheric oxidation, resulting in formation of a dense, firmly adherent dark oxide glaze over the surface thereof, and by subsequent- 1y lubricating the article by applying an ungent thereto, and passing it through dies at temperatures such as result from the work of friction and deformation; the improvement which comprises subjecting the surface, still coated with said oxide glaze, preparatory to lubricating it for a pass through the dies, to the action of a fused substantially anhydrous bath composed of caustic soda containing 5 to per cent of sodium nitrate, at

400 to 600 0., for a time sufficient to convert the glaze to a coating with a mat surface having lubricant-retaining properties.

4. In the drawing of tubes, rods, wires and the like, of "stainless steel, by passing the same through rolls at elevated temperatures, while exposed to atmospheric oxidation, resulting in formation of a dense, firmly adherent dark oxide glaze over the surface thereof, and by subsequently lubricating the article-by applying an ungent thereto, and passing it through dies at temperatures such a result from the work of friction and a deformation; the improvement which comprise subjecting the surface, still coated with said oxide glaze, preparatory to lubricating it for a pass through the dies, to the action of a fused substantially anhydrous bath composed of caustic soda containing 5 to 15 per cent of potassium dichromate, at 400 to 600 C., for a time sufficient to convert the glaze to a coating with a mat surface having lubricant-retaining properties.

5. In the drawing of tubes, rods, wires and the like, of stainless" steel, by passing the same through rolls at elevated temperatures, while exposed to atmospheric oxidation, resulting in formation of a dense, firmly adherent dark oxide glaze over the surface thereof, and by subsequently lubricating the article, by applying an ungent thereto, and passing it through dies at temperatures such as result from the work of friction and deformation; the improvement which comprises subjecting the surface, still coated with said oxide glaze, preparatory to lubricating it for a pass through the dies, to the action of a fused substantially anhydrous bath composed of caustic soda containing 5 to 15 per cent of potassium permanganate, at 400 to 600 0., for a time sufficient to convert the glaze to a coating with a mat surface having lubricant-retaining properties.

HARRY R. SPENCE'. HORACE W. HOOKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,467,398 Schumacher Sept. 11, 1923 2,271,375 McKay .Ian. 27, 1942 2,369,596 Millen Feb. 13, 1945 2,370,959 Holden Mar. 6, 1945 

